CD5(-) diffuse large B-cell lymphoma with peculiar cyclin D1+ phenotype. Pathologic and molecular characterization of a single case.

Increased expression of cyclin D1 is notoriously associated with mantle cell lymphoma because of translocation t(11;14)(q13;q32) or variants involving the cyclin D1 gene. We present an unusual case of CD5-negative diffuse large B-cell lymphoma expressing cyclin D1 in the absence of translocation by fluorescence in situ hybridization analysis. Using array-comparative genomic hybridization, we found a complex karyotype without the characteristic chromosomal aberrations accompanying cyclin D1 translocation in mantle cell lymphoma; instead, there was monoallelic deletion of AKT interacting protein and glycogen synthase kinase-3 β genes, both involved in the AKT/glycogen synthase kinase-3 β cascade-controlling nuclear levels of cyclin D1. These findings suggest that posttranslational events regulating cyclin D1 activity may take place also in a subset of diffuse large B-cell lymphomas and contribute to lymphomagenesis. As a consequence, the sole cyclin D1 positivity by immunohistochemistry may not be enough to distinguish pleomorphic/blastoid mantle cell lymphoma from diffuse large B-cell lymphoma. Search for t(11;14) with fluorescence in situ hybridization probes should always be performed in doubtful cases.